Odour control at biowaste composting facilities

There are several options to effectively reduce odorous emissions at composting facilities depending on the type of composting system used. Some of the more relevant measures for open and enclosed composting facilities are presented in this article. Results from different investigations on odour reduction efficiencies of biological waste gas treatment systems at various scales are presented. Biofilter/bioscrubber combinations were used and different biofilter materials were tested. The more relevant odorous substances in the waste gas were identified, and their reduction in the different systems was measured. The biofilter proved to be mainly responsible for efficient odour degradation. The investigations presented in this article revealed that screened compost was very effective, and proved to be a low cost biofilter material for odour degradation purposes. Screened compost showed higher degradation rates than a coke-compost mixture newly developed by the University of Leipzig. Furthermore, it seems that enclosed systems have advantages when compared to conventional open single bed biofilters.     

Analytical determination of the suitability of different processes for the treatment of odorous waste gas

In order to determine the efficiency of different treatment systems for the reduction of odorous emissions, a gas chromatographic method followed by simultaneous mass spectrometry and olfactometry (GC-MS/O) was developed. Samples from a coffee bean roasting and a fat and oil processing plant were analyzed, respectively. The results were compared with the data obtained by olfactometric measurements. At a coffee bean roasting plant, cooling gases were analyzed prior to and after treatment in a full scale bioscrubber. The GC-MS/O analysis showed that the amounts of aldehydes and ketones decreased after treatment of cooling gases of coffee bean roasting in the bioscrubber, whereas the contents of the heterocyclic compounds, like pyridine and the pyrazines, and acetophenone and guaiacol remained almost unchanged. The amounts of dimethyl disulfide, 3-hydroxy-2-butanone, and the carboxylic acids increased after bioscrubber treatment. Furthermore, the performance of each stage of a combined experimental plant for the treatment of exhaust air of fat and oil processing was investigated. This treatment plant consisted of a bioscrubber, a biofilter, and an activated carbon adsorber. The important odor-active compounds of the exhaust air of fat and oil processing were the typical fat oxidation products (aldehydes, ketones) and with lower importance 2-pentylfuran, a few terpenes and aromates. Again, the key odor-active compounds, aldehydes and ketones, were degraded in the bioscrubber. Further degradation of aliphatic, unsaturated, methylated, and cyclic alkanes, as well as aromates, terpenes, and furans by the biofilter was observed. After the last treatment stage, the activated carbon filter, only small amounts of aliphatic, unsaturated, methylated, and cyclic alkanes and aromates remained in the waste gas. For both applications, the results of the developed GC-MS/O method correlated very well with olfactometric measurements.     

Development of a simple and sensitive method for the characterization of odorous waste gas emissions by means of solid-phase microextraction (SPME) and GC-MS/olfactometry

A solid-phase microextraction (SPME) method has been developed for the extraction of odorous compounds from waste gas. The enriched compounds were characterized by gas chromatography-mass spectrometry (GC-MS) and gas chromatography followed by simultaneous flame ionization detection and olfactometry (GC-FID/O). Five different SPME fiber coatings were tested, and the carboxen/polydimethylsiloxane (CAR/PDMS) fiber showed the highest ability to extract odorous compounds from the waste gas. Furthermore, parameters such as exposure time, desorption temperature, and desorption time have been optimized. The SPME method was successfully used to characterize an odorous waste gas from a fat refinery prior to and after waste gas treatment in order to describe the treatment efficiency of the used laboratory scale plant which consisted of a bioscrubber/biofilter combination and an activated carbon adsorber. The developed method is a valuable approach to provide detailed information of waste gas composition and complements existing methods for the determination of odors. However, caution should be exercised if CAR/PDMS fibers are used for the quantification of odorous compounds in multi-component matrices like waste gas emissions since the relative affinity of each analyte was shown to differ according to the total amount of analytes present in the sample.     

Green house gas emissions from composting and mechanical biological treatment.

In order to carry out life-cycle assessments as a basis for far-reaching decisions about environmentally sustainable waste treatment, it is important that the input data be reliable and sound. A comparison of the potential greenhouse gas (GHG) emissions associated with each solid waste treatment option is essential. This paper addresses GHG emissions from controlled composting processes. Some important methodological prerequisites for proper measurement and data interpretation are described, and a common scale and dimension of emission data are proposed so that data from different studies can be compared. A range of emission factors associated with home composting, open windrow composting, encapsulated composting systems with waste air treatment and mechanical biological waste treatment (MBT) are presented from our own investigations as well as from the literature. The composition of source materials along with process management issues such as aeration, mechanical agitation, moisture control and temperature regime are the most important factors controlling methane (CH4), nitrous oxide (N2O) and ammoniac (NH3) emissions. If ammoniac is not stripped during the initial rotting phase or eliminated by acid scrubber systems, biofiltration of waste air provides only limited GHG mitigation, since additional N2O may be synthesized during the oxidation of NH3, and only a small amount of CH4 degradation occurs in the biofilter. It is estimated that composting contributes very little to national GHG inventories generating only 0.01-0.06% of global emissions. This analysis does not include emissions from preceding or post-treatment activities (such as collection, transport, energy consumption during processing and land spreading), so that for a full emissions account, emissions from these activities would need to be added to an analysis.     

Assessment of the environmental impact of management measures for the biodegradable fraction of municipal solid waste in São Paulo City

There is increasing concern about landfilling of biodegradable wastes. Therefore, biological treatment processes such as composting and biogasification have been considered as alternative strategies for managing those wastes. In this work, life cycle assessment was employed to compare the environmental impacts of landfilling, composting, and biological treatment of municipal solid waste in S?o Paulo City, Brazil. Energy consumption, recovered resources, and emissions to air and water were quantified and analyzed in terms of their potential contribution to global warming, acidification, and nutrient enrichment impact. The results demonstrated that processes that require high levels of energy consumption, such as wastewater treatment, play an important role in the outcome of environmental impact potentials. It was found that the landfilling of all waste is generally the worst strategy from an environmental point of view. However, significant reductions in the resulting impacts can be accomplished through biogasification and composting of the biodegradable fraction. Regarding composting, the application of a biofilter for gas treatment reduced significantly the gaseous emissions.     

Increase of the purification efficiency of biofilters by the use of a complementary ionisation step

The biofilter and the ionisation system are two oxidative treatment techniques for purification of waste gas streams with low concentrations of volatile organic compounds. In this paper, the authors present the investigations of an ionisation technique aimed at increasing the efficiency of the reduction of the odorant concentration in waste gas streams from biological waste treatment plants. The objective is to enable advanced odour emission reduction and to adjust the existing biofilters to stricter requirements. In a first step, the odorous substances which are major contributors to the overall odorant concentration are identified on basis of various emission data sets with the help of a method of life cycle impact assessment. Thereby limonene, alpha-pinene, ethyl butyrate and dimethyl disulphide were identified as crucial indicators. In a second step, experimental investigations using limonene as a model compound were conducted to gain an understanding of the ionisation process itself and at last for the evaluation of the system.     

生物膜法处理挥发性有机化合物技术

综述了生物法有机废气处理技术的国内外研究现状,介绍了生物膜法处理VICs的装置及工艺流程。重点讨论了生物滤池和生物滴滤池在设计和运行中存在的问题及填料、生物量、湿度、pH和营养物质等主要影响因素。     

Control of GHG emission at the microbial community level

All organic material eventually is decomposed by microorganisms, and considerable amounts of C and N end up as gaseous metabolites. The emissions of greenhouse relevant gases like carbon dioxide, methane and nitrous oxides largely depend on physico-chemical conditions like substrate quality or the redox potential of the habitat. Manipulating these conditions has a great potential for reducing greenhouse gas emissions. Such options are known from farm and waste management, as well as from wastewater treatment. In this paper examples are given how greenhouse gas production might be reduced by regulating microbial processes. Biogas production from manure, organic wastes, and landfills are given as examples how methanisation may be used to save fossil fuel. Methane oxidation, on the other hand, might alleviate the problem of methane already produced, or the conversion of aerobic wastewater treatment to anaerobic nitrogen elimination through the anaerobic ammonium oxidation process might reduce N2O release to the atmosphere. Changing the diet of ruminants, altering soil water potentials or a change of waste collection systems are other measures that affect microbial activities and that might contribute to a reduction of carbon dioxide equivalents being emitted to the atmosphere.     

恶臭气体生物处理技术研究进展

介绍了恶臭气体的种类、危害、特征、处理方法及原理；概述了恶臭气体的3种主要生物处理方法：生物滤池、生物滴滤池和生物洗涤器，介绍3种方法的工艺流程、技术特点及最新研究进展；提出了生物法处理恶臭气体亟需解决的问题及研究方向。     

Cost effective waste management through composting in Africa

Greenhouse gas (GHG) emissions per person from urban waste management activities are greater in sub-Saharan African countries than in other developing countries, and are increasing as the population becomes more urbanised. Waste from urban areas across Africa is essentially dumped on the ground and there is little control over the resulting gas emissions. The clean development mechanism (CDM), from the 1997 Kyoto Protocol has been the vehicle to initiate projects to control GHG emissions in Africa. However, very few of these projects have been implemented and properly registered. A much more efficient and cost effective way to control GHG emissions from waste is to stabilise the waste via composting and to use the composted material as a soil improver/organic fertiliser or as a component of growing media. Compost can be produced by open windrow or in-vessel composting plants. This paper shows that passively aerated open windrows constitute an appropriate low-cost option for African countries. However, to provide an usable compost material it is recommended that waste is processed through a materials recovery facility (MRF) before being composted. The paper demonstrates that material and biological treatment (MBT) are viable in Africa where they are funded, e.g. CDM. However, they are unlikely to be instigated unless there is a replacement to the Kyoto Protocol, which ceases for Registration in December 2012.     

Possibilities and limitations of life cycle assessment (LCA) in the development of waste utilization systems – Applied examples for a region in Northern Germany

Against the background of increasing concerns about climate change, the reduction of greenhouse gas emissions has become an integral part of processes in both the waste management and the energy industries. This is reflected in the development of new waste treatment concepts, in which domestic and commercial waste is treated with the aim of utilizing its energy content, while at the same time recycling as much of its material content as possible. Life cycle assessment (LCA) represents a method of assessing the environmental relevance of a waste management system, the basis of which is a material flow analysis of the system in question. GHG emissions from different options for thermal treatment and energy recovery from waste as applied to a region in Northern Germany have been analyzed by the LCA approach and an indicative LCA, which only considers those emissions resulting from operating stages of the system. Operating stages have the main share of emissions compared to pre-processing stages. Results show that through specific separation of waste material flows and highly efficient energy recovery, thermal treatment and energy generation from waste can be optimized resulting in reduction of emissions of greenhouse gases. There are also other areas of waste utilization, currently given little attention, such as the solar drying of sewage sludge, which can considerably contribute to the reduction of greenhouse gas emissions.     

Role of waste management with regard to climate protection: a case study.

According to the Kyoto Protocol and the burden-sharing agreement of the European Union, Austria is required to cut greenhouse gas (GHG) emissions during the years 2008 to 2012 in order to achieve an average reduction of 13%, based on the level of emissions for the year 1990. The present contribution gives an overview of the history of GHG emission regulation in Austria and identifies the progress made towards the realization of the national climate strategy to attain the GHG emission targets. The contribution uses Austria as an example of the way in which proper waste management can help to reduce GHG emissions. The GHG inventories show that everything must be done to minimize the carbon input due to waste deposition at landfill sites. The incineration of waste is particularly helpful in reducing GHG emissions. The waste-to-energy by incineration plants and recovery of energy yield an ecologically proper treatment of waste using state-of-the-art techniques of a very high standard. The potential for GHG reduction of conventional waste treatment technologies has been estimated by the authors. A growing number of waste incinerators and intensified co-incineration of waste in Austrian industry will both help to reduce national GHG emissions substantially. By increasing the number and capacity of plants for thermal treatment of waste the contribution of proper waste management to the national target for reduction of GHG emissions will be in the range of 8 to 14%. The GHG inventories also indicate that a potential CO2 reduction of about 500 000 t year(-1) is achievable by co-incineration of waste in Austrian industry.     

Changes in carbon and nitrogen pool during in-situ aeration of old landfills under varying conditions

Emissions from old landfills via leachate and the gas phase are influenced by state and stability of the organic matter in the solid waste and by environmental conditions within the landfill. Remediation of landfills by means of in-situ aeration is one possibility to reduce these emissions. By establishing aerobic conditions, biological processes in the landfill are accelerated. To investigate the effects of this remediation technology, lab-scale experiments with column tests have been carried out. The main goal of the present work is to characterize the changes of the carbon and nitrogen compounds in the aerated solid waste, the leachate and the gas phase under varying conditions. The results demonstrate a clear reduction of emissions and a stabilization of the organic matter. Furthermore, it is shown that both the intensity of aeration and the amount of water affect biological processes to a certain extent. Even when columns were operated under anaerobic conditions after a long running period of aeration, the emissions remained low.     

Sustainable waste management in Africa through CDM projects

Only few Clean Development Mechanism (CDM) projects (traditionally focussed on landfill gas combustion) have been registered in Africa if compared to similar developing countries. The waste hierarchy adopted by many African countries clearly shows that waste recycling and composting projects are generally the most sustainable. This paper undertakes a sustainability assessment for practical waste treatment and disposal scenarios for Africa and makes recommendations for consideration. The appraisal in this paper demonstrates that mechanical biological treatment of waste becomes more financially attractive if established through the CDM process. Waste will continue to be dumped in Africa with increasing greenhouse gas emissions produced, unless industrialised countries (Annex 1) fund carbon emission reduction schemes through a replacement to the Kyoto Protocol. Such a replacement should calculate all of the direct and indirect carbon emission savings and seek to promote public–private partnerships through a concerted support of the informal sector.     

Odour management and treatment technologies: an overview

There is a large variety of options available for the effective treatment of odorous emissions. The most important physical, chemical and biological treatment processes are shortly described and their favourable applications, as well as their limits, are highlighted. But for a sustainable solution of an industrial odour problem, there is more involved than just the installation of a waste gas treatment system. This article focuses on a general and systematic approach towards extensive odour management. First of all, an odour assessment should be worked out where all actual and potential odour emission sources are recorded and characterised. A special focus should be set on fugitive emissions, which may have an enormous impact on the overall odour problem. They need to be captured before they can be supplied to a treatment system. According to the composition and condition of the waste gases, an appropriate treatment system must be selected. For this purpose, test systems have been developed and are presented in this article.     

Microbial oxidation of methane from old landfills in biofilters

Landfill gas emissions are among the largest sources of the greenhouse gas methane. For this reason, the possibilities of microbial methane degradation in biofilters were investigated. Different filter materials were tested in two experimental plants, a bench-scale plant (total filter volume 51 l) and a pilot plant (total filter volume 4 m3). Three months after the beginning of the experiment, very high degradation rates of up to 63 g CH4/(m3h) were observed in the bench-scale plant at mean methane concentrations of 2.5% v/v and with fine-grained compost as biofilter material. However, the degradation rates of the compost biofilter decreased in the fifth month of the experiment, probably due to the accumulation of exopolymeric substances formed by the microorganisms. A mixture of compost, peat, and wood fibers showed stable and satisfactory degradation rates around 20 g/(m3h) at mean concentrations of 3% v/v over a period of one year. In this material, the wood fibers served as a structural material and prevented clogging of the biofilter. Extrapolation of the experimental data indicates that biofilters for methane oxidation have to be at least 100 times the volume of biofilters for odor control to obtain the same cleaning efficiency per unit volume flow of feed gas.     

Mitigation of global greenhouse gas emissions from waste: conclusions and strategies from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. Working Group III (Mitigation).

Greenhouse gas (GHG) emissions from post-consumer waste and wastewater are a small contributor (about 3%) to total global anthropogenic GHG emissions. Emissions for 2004-2005 totalled 1.4 Gt CO2-eq year(-1) relative to total emissions from all sectors of 49 Gt CO2-eq year(-1) [including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and F-gases normalized according to their 100-year global warming potentials (GWP)]. The CH4 from landfills and wastewater collectively accounted for about 90% of waste sector emissions, or about 18% of global anthropogenic methane emissions (which were about 14% of the global total in 2004). Wastewater N2O and CO2 from the incineration of waste containing fossil carbon (plastics; synthetic textiles) are minor sources. Due to the wide range of mature technologies that can mitigate GHG emissions from waste and provide public health, environmental protection, and sustainable development co-benefits, existing waste management practices can provide effective mitigation of GHG emissions from this sector. Current mitigation technologies include landfill gas recovery, improved landfill practices, and engineered wastewater management. In addition, significant GHG generation is avoided through controlled composting, state-of-the-art incineration, and expanded sanitation coverage. Reduced waste generation and the exploitation of energy from waste (landfill gas, incineration, anaerobic digester biogas) produce an indirect reduction of GHG emissions through the conservation of raw materials, improved energy and resource efficiency, and fossil fuel avoidance. Flexible strategies and financial incentives can expand waste management options to achieve GHG mitigation goals; local technology decisions are influenced by a variety of factors such as waste quantity and characteristics, cost and financing issues, infrastructure requirements including available land area, collection and transport considerations, and regulatory constraints. Existing studies on mitigation potentials and costs for the waste sector tend to focus on landfill CH4 as the baseline. The commercial recovery of landfill CH4 as a source of renewable energy has been practised at full scale since 1975 and currently exceeds 105 Mt CO2-eq year(-1). Although landfill CH4 emissions from developed countries have been largely stabilized, emissions from developing countries are increasing as more controlled (anaerobic) landfilling practices are implemented; these emissions could be reduced by accelerating the introduction of engineered gas recovery, increasing rates of waste minimization and recycling, and implementing alternative waste management strategies provided they are affordable, effective, and sustainable. Aided by Kyoto mechanisms such as the Clean Development Mechanism (CDM) and Joint Implementation (JI), the total global economic mitigation potential for reducing waste sector emissions in 2030 is estimated to be > 1000 Mt CO2-eq (or 70% of estimated emissions) at costs below 100 US$ t(-1) CO2-eq year(-1). An estimated 20-30% of projected emissions for 2030 can be reduced at negative cost and 30-50% at costs < 20 US$ t(-) CO2-eq year(-1). As landfills produce CH4 for several decades, incineration and composting are complementary mitigation measures to landfill gas recovery in the short- to medium-term--at the present time, there are > 130 Mt waste year(-1) incinerated at more than 600 plants. Current uncertainties with respect to emissions and mitigation potentials could be reduced by more consistent national definitions, coordinated international data collection, standardized data analysis, field validation of models, and consistent application of life-cycle assessment tools inclusive of fossil fuel offsets.     

Life-cycle-assessment of the historical development of air pollution control and energy recovery in waste incineration

Incineration of municipal solid waste is a debated waste management technology. In some countries it is the main waste management option whereas in other countries it has been disregarded. The main discussion point on waste incineration is the release of air emissions from the combustion of the waste, but also the energy recovery efficiency has a large importance.The historical development of air pollution control in waste incineration was studied through life-cycle-assessment modelling of eight different air pollution control technologies. The results showed a drastic reduction in the release of air emissions and consequently a significant reduction in the potential environmental impacts of waste incineration. Improvements of a factor 0.85–174 were obtained in the different impact potentials as technology developed from no emission control at all, to the best available emission control technologies of today (2010).The importance of efficient energy recovery was studied through seven different combinations of heat and electricity recovery, which were modelled to substitute energy produced from either coal or natural gas. The best air pollution control technology was used at the incinerator. It was found that when substituting coal based energy production total net savings were obtained in both the standard and toxic impact categories. However, if the substituted energy production was based on natural gas, only the most efficient recovery options yielded net savings with respect to the standard impacts. With regards to the toxic impact categories, emissions from the waste incineration process were always larger than those from the avoided energy production based on natural gas. The results shows that the potential environmental impacts from air emissions have decreased drastically during the last 35 years and that these impacts can be partly or fully offset by recovering energy which otherwise should have been produced from fossil fuels like coal or natural gas.     

Carbon--making the right choice for waste management in developing countries

Due to initiatives such as the clean development mechanism (CDM), reducing greenhouse gas emissions for a developing country can offer an important route to attracting investment in a variety of qualifying project areas, including waste management. To date CDM projects have been largely confined to schemes that control emission from landfill, but projects that avoid landfilling are beginning to be submitted. In considering the waste options which might be suitable for developing countries certain ones, such as energy from waste, have been discounted for a range of reasons related primarily to the lack of technical and other support services required for these more sophisticated process trains. The paper focuses on six options: the base case of open dumping; three options for landfill (passive venting, gas capture with flaring, and gas capture with energy production), composting and anaerobic digestion with electricity production and composting of the digestate. A range of assumptions were necessary for making the comparisons based on the effective carbon emissions, and these assumptions will change from project to project. The highest impact in terms of carbon emissions was from using a sanitary landfill without either gas flaring or electricity production; this was worse than the baseline case using open dumpsites. Landfills with either flaring or energy production from the collected gas both produced similar positive carbon emissions, but these were substantially lower than both open dumping and sanitary landfill without flaring or energy production. Composting or anaerobic digestion with energy production and composting of the digestate were the two best options with composting being neutral in terms of carbon emissions and anaerobic digestion being carbon negative. These generic conclusions were tested for sensitivity by modifying the input waste composition and were found to be robust, suggesting that subject to local study to confirm assumptions made, the opportunity for developing CDM projects to attract investment to improved waste management infrastructure is significant. Kyoto credits in excess of 1 tCO2e/t of waste could be realised.     

Passive drainage and biofiltration of landfill gas: results of Australian field trial

A field scale trial was undertaken at a landfill site in Sydney, Australia (2004-2008), to investigate passive drainage and biofiltration of landfill gas as a means of managing landfill gas emissions from low to moderate gas generation landfill sites. The objective of the trial was to evaluate the effectiveness of a passive landfill gas drainage and biofiltration system at treating landfill gas under field conditions, and to identify and evaluate the factors that affect the behaviour and performance of the system.The trial results showed that passively aerated biofilters operating in a temperate climate can effectively oxidise methane in landfill gas, and demonstrated that maximum methane oxidation efficiencies greater than 90% and average oxidation efficiencies greater than 50% were achieved over the 4 years of operation. The trial results also showed that landfill gas loading was the primary factor that determined the behaviour and performance of the passively aerated biofilters. The landfill gas loading rate was found to control the diffusion of atmospheric oxygen into the biofilter media, limiting the microbial methane oxidation process. The temperature and moisture conditions within the biofilter were found to be affected by local climatic conditions and were also found to affect the behaviour and performance of the biofilter, but to a lesser degree than the landfill gas loading.